1. Field of the Invention
The present invention relates to a battery control device of a hybrid forklift truck, the truck having a traveling section for driving wheels by means of either or both of an engine (such as an internal combustion engine) and a battery-operated motor generator, and a cargo handling section provided with actuators driven by means of either or both of the engine and the battery-operated motor generator to perform lifting up-and-down of cargos, the battery control device controlling discharge/charge current from/to the battery so that excessive exhaustion or excessive charging does not occur in the battery, and a hybrid forklift truck equipped with the battery control device.
2. Description of the Related Art
In recent years, hybrid power units are adopted as high-efficient driving means of forklift trucks.
Such a hybrid power unit comprises a traveling section for driving traveling wheels by means of either or both of an engine such as an internal combustion engine and a battery-operated electric motor and a cargo handling section provided with an actuators driven by means of either or both of the engine and the battery-operated electric motor and an oil hydraulic motor for recovering potential energy of a lifted cargo when the cargo is lifted down, and the engine or electric motor or engine plus electric motor is selectively used as driving means depending on operating conditions of the forklift truck.
FIG. 8 is a schematic representation of the driving system of such a hybrid forklift truck.
In FIG. 8, reference numeral 1 is a battery, 2 indicates actuators for driving the forklift truck in travel and cargo handling operation, 3 is an engine such as an internal combustion engine, 4 is a motor generator, 6 is a power transmission device mechanically connecting the engine 1, the motor generator 4, and the actuator 2, 5 is an inverter electrically connecting the battery 1 to the motor generator 4.
Reference numeral 010 is a device for estimating remaining capacity of battery 1 based on detected voltage and current of the battery 1. Reference numeral 100 is a controller which includes the device 010 for estimating remaining capacity of battery 010 and outputs an operation control directive to the engine 3 and an operation control directive to the motor generator 4 via the inverter 5.
In the hybrid forklift truck, remaining capacity of the battery 1 (hereafter referred to as SOC (state of charge) of battery) in operation is estimated by the battery SOC estimating device 010 based on detected voltage and integrated current discharged from the battery 1 to the motor generator 4.
In Japanese Patent Gazette No. 3304507 (patent literature 1) discloses a remaining capacity meter of a battery, with which the remaining capacity is determined based on detected voltage and current of the battery and integrated value of current.
In Japanese Laid-Open Patent Application No. 6-59002 (patent literature 2) disclosed a remaining capacity determining method of a battery, with which voltage and current of the battery are measured in accordance with conditions determined and stored in an environment file and remaining capacity of the battery is determined using a correlation table defining relationship between remaining capacity and voltage of battery with discharge current as a parameter.
In a hybrid forklift truck, there occur problems that deterioration of the battery is enhanced when battery SOC, i.e. remaining capacity of the battery is too low and that battery voltage rises extremely when a state that battery SOC is higher than a certain permissible value continues.
Further, as discharging from and charging to the battery occur at frequent intervals in the hybrid forklift truck, the error in estimation of SOC of the battery increases when the SOC is estimated by the battery control device 010 based on voltage and integrated current of the battery 1 as is in the conventional art shown in FIG. 8 caused by battery conditions such as temperature and so on. There has been proposed means to compensate the errors in estimation of SOC of the battery, however, there would be considerable difficulty in raising accuracy of estimation of SOC of battery under the circumstance the battery is used with short stop time of charging and discharging.
Further, when energy is recovered from actuators for traveling operation and cargo handling operation concurrently, there may occur cases that remaining capacity of the battery is high and power possible to be charged to the battery is too small to receive all of the recovered energy or that power possible to be released from the battery is small and required power can not be supplied from the battery, if SOC of the battery is not controlled appropriately. Therefore, it is demanded that allocation of drive power to drive the actuators to the engine and/or battery-operated motor is determined in consideration of power possible (permissible) to be released from the battery. However, the conventional art of estimating SOC of the battery based on voltage and integrated current of the battery as shown in FIG. 8 can not cater to such a demand.
In the patent literatures 1 and 2, means to detect remaining capacity of battery accurately is disclosed, however, an art to link the accurate estimation of SOC of the battery to control allocation of drive power to drive the actuators to the engine and/or battery-operated motor so that excessive exhaustion or excessive charging does not occur in the battery of a hybrid forklift truck is not disclosed.